A fuel cell is an electricity generation cell that generates electricity via a reaction involving hydrogen and oxygen. Such a fuel cell has advantages in that it may continuously generate electricity as long as oxygen and hydrogen are supplied, unlike general chemical cells such as, for example, a battery or a storage battery, and in that it has no thermal loss and is twice as efficient as an internal combustion engine. In addition, the fuel cell entails low emission of pollutants because it directly converts chemical energy produced via the reaction of hydrogen and oxygen into electricity. Accordingly, the fuel cell has advantages in that it is environmentally friendly and is capable of reducing the risk of resource depletion due to increased energy consumption. Fuel cells may be broadly classified, according to the type of electrolyte used therein, into a polymer electrolyte membrane fuel cell (PEMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), and an alkali fuel cell (AFC), for example. These respective fuel cells basically operate on the same principle, but differ in, for example, the type of fuels used, the operating temperatures thereof, catalysts and electrolytes. Among the aforementioned fuel cells, the polymer electrolyte membrane fuel cell is known to be the most promising in small-scale stationary power generation equipment as well as transportation systems because it operates at a lower temperature than other fuel cells and may be reduced in size owing to a large output density thereof.
One of the most important factors to improve the performance of the polymer electrolyte membrane fuel cell is to allow a polymer electrolyte membrane or a proton exchange membrane (PEM) of a membrane-electrode assembly (MEA) to maintain a constant percentage of moisture content by supplying at least predetermined amount of moisture thereto. This is because electricity generation efficiency is rapidly deteriorated when the polymer electrolyte membrane is dried. Examples of methods of humidifying the polymer electrolyte membrane may include a bubbler humidification method of supplying moisture by passing a subject gas via a diffuser after a pressure vessel is filled with water, a direct injection method of calculating the supply amount of moisture required for a fuel cell reaction and directly supplying moisture to a gas flow pipe through a solenoid valve, and a humidification membrane method of supplying moisture to a gas flow layer using a polymer separation membrane. Among these methods, the humidification membrane method of humidifying a polymer electrolyte membrane by supplying water vapor to gas supplied to the polymer electrolyte membrane using a membrane that selectively permeates only water vapor contained in exhaust gas is advantageous in terms of a reduction in weight and size.
The selective permeation membrane used in the humidification membrane method may be a hollow fiber membrane having a large permeation area per unit volume when it forms a module. That is, when a humidifier is manufactured using a hollow fiber membrane, a hollow fiber membrane having a wide contact surface area may be highly integrated, thus realizing sufficient humidification of a fuel cell even for a small volume thereof. In addition, low-cost materials are available, and moisture and heat contained in high-temperature unreacted gas, discharged from the fuel cell, may be collected to thereby be reused via the humidifier.
However, in the case of a conventional hollow fiber membrane module, when a plurality of hollow fiber membranes is integrated in order to increase the capacity of the module, a gas stream moving outward from the hollow fiber membranes may not be uniformly formed due to inconsistent resistance caused by the hollow fiber membranes. A technique of or increasing the capacity by splitting a hollow fiber membrane bundle or forming a unit module in a cartridge shape has been used in order to overcome the problem described above. However, this technique may cause an increase in the manufacturing cost because the time required to manufacture an individual cartridge module is too long, or may increase variation in quality due to poor workability when the bundle is split.